In conventional thermal transcription recording methods, using melting-type thermal transcription ink sheet wherein pigment is employed as coloring stuff, or sublimation-type thermal transcription ink sheet wherein thermal diffusion dyestuff is employed as coloring stuff, an image is formed direct on a recording sheet by a recording head through the ink sheet overlaid on the recording sheet. Also, such other method is known, where, in order to obtain a quality image irrespective of the kind of recording sheet (surface material, surface condition), an image is once formed on an intermediate sheet by any desired method, including thermal transcription, and then the image on intermediate sheet is transcribed on a recording sheet as the ultimate image.
An example of thermal transcription recording method/apparatus using an intermediate sheet is the one which is laid open by the gazette of Japanese Patent Application Toku.cndot.Kai.cndot.Hei 4-327981. In the following, constitution of this method is explained, referring to FIG. 15.
FIG. 15 shows the outline constitution of a thermal transcription recording apparatus. Where, the intermediate sheet 301 is made of a heat resisting first substrate 302 and a dye depositing layer 303. Ink sheet 304 is made, likewise, of a heat resisting second substrate 305 and an ink material layer 306.
The intermediate sheet 301 and ink sheet 304 are placed, being pressed together, between platen 307 and thermal head 308, which selectively generates heat in response to a recording signal to transcribe at least part of coloring stuff contained in the ink material layer 306 onto the surface of dye depositing layer 303 of intermediate sheet 301; an image is thus recorded on the intermediate sheet 301. The image-bearing intermediate sheet 301 is carried forward to the direction of 309 by revolution of the platen 307. Ink sheet 304 is rolled up by ink sheet roll up roller 310.
In recording a color image, the platen 307 is reversed upon completion of the recording with a first color to bring the intermediate sheet 301 back to the starting position to be ready for recording with a second color. During the reversing operation, the thermal head 308 and ink sheet 304 are held off the intermediate sheet 301. For the second color recording, they are reset together to make contact with a pressure, and recording is conducted in the same manner as in the first color. By the same procedure, image with a third color (being the final color) is recorded.
Next step is to overlay the intermediate sheet 301 on recording sheet 311 to be press-held between heating roller 312 and roller 313. Then the intermediate sheet 301 is heated with the heating roller 312, the dye depositing layer 303 softens, and part of it diffuses into the surface of the recording sheet 311. By means of separation roller 314 and roller 315, the first substrate sheet 302 is made to go straight forward, while the recording sheet 311 is bent; by this way, the dye depositing layer 303 is transcribed on the recording sheet 311. And then, the recording sheet 311 carrying the dye depositing layer 303 over it goes through pressure roller 316 and roller 317 to have the recorded image fixed.
Thus, in the thermal transcription recording using the intermediate sheet 301, melting type thermal transcription method needs an intermediate sheet 301 having a dye depositing layer 303 into which coloring stuff fuses; or, sublimation type thermal transcription method needs an intermdeiate sheet 301 having a dye depositing layer 303 to which dyestuff adheres. Formation of an image on the recording sheet 311 is conducted by once forming the image on the dye depositing layer 303 of intermediate sheet 301, and then transcribing the image onto the recording sheet 311 by overlaying the dye depositing layer 303 carrying the image on the recording sheet 311; then, the recording sheet 311 having the dye depositing layer 303 affixed on it is separated from the first substrate 302 of the intermediate sheet 301; afterwards, a fixing process follows depending on needs.
When forming a color image consisting of plurality of color elements in such conventional process constitution, an image has to be recorded on the dye depositing layer 303 of intermediate sheet 301 for each color, superpositioning second and third colors on the image of first color. Images of the second color and after need to be exactly aligned on the first image. Inaccurate aligning results in the poor color reproduction, blurred images and other drawbacks. Furthermore, in the conventional method, if relative speed between the ink sheet 304 and the intermediate sheet is not kept constant, various inconveniences such as uneven recording density and broken ink sheet arise.
The intermediate sheet 301 in the conventional constitution is transferred by a friction driving force of platen 307 and a friction between the ink material layer of the ink sheet 304 and the dye depositing layer 303 of intermediate sheet 301. On the other hand, the ink sheet 304 is driven by a pulling force of the ink sheet roll up roller 310, and a friction between the ink material layer 306 of ink sheet 304 and the dye depositing layer 303 of intermediate sheet 301; also, the back tension by ink dispenser roller (not illustrated) and the brake force caused by a friction between the thermal head 308 and back surface of the ink sheet 304 are effected. The ink sheet 304 and the intermediate sheet 301 are transferred by virture of a subtle balancing among these forces, maintaining an appropriate tension. Dependence of the transfer of intermediate sheet 301 and ink sheet 304, being most important elements, on the friction coefficient, which is easily influenced by temperature/moisture, has been making it difficult to secure a stable transfer of these sheets.
The color image recording apparatus by means of thermal transcription uses an ink sheet on which ink materials of three colors, viz. yellow, magenta and cyanine, plus black, making four colors, are provided sequentially in one space after another, and transcribes the ink sheet sequentially on a recording sheet, or on an intermediate sheet, to form a color image. On the ink sheet and coatings of each of the color ink materials provided sequentially over the full space to comply with the largest size of recording sheet. Consequently, when the size of recording sheet is small, part of the ink is left unused, rendering the utilization rate of ink sheet low.
In a method where an intermediate sheet having a dye depositing layer, the size of which is adapted to fit for the size of recording sheet, is used, the intermediate sheet needs to be replaced each time when the size of recording sheet is changed; the work efficiency is affected.
In another case, where an intermediate sheet on which the dye depositing layer is provided to comply with the largest size recording sheet, or an intermediate sheet on which the dye depositing layer is provided over the entire surface is used, and the dye depositing layer having an image is transcribed on a recording sheet of any desired size, and then separate the recording sheet having the transcribed dye depositing layer with it from the substrate sheet of intermediate sheet, when the size of recording sheet is larger than the intermediate sheet the cutting performance of dye depositing layer at the front and the rear ends of the recording sheet is poor, when the size of recording sheet is smaller than the intermediate sheet the cutting performance not only at the front and rear, but also at both sides turns out to be poor, causing difficulty in separation of the recording sheet, and other problems.